This invention relates generally to apparatus for applying and releasing a vehicular parking brake. Typically, such apparatus includes a control with a foot-operated lever or pedal which, when depressed, acts to turn a toothed sector and apply tension to a cable in order to set the parking brake of the vehicle. Once the brake has been set, a pawl engages and holds the sector to prevent the return springs of the brake and the brake clamp load from effecting release of the brake.
More specifically, the invention relates to a self-adjusting, push-to-release parking brake control. A self-adjusting control includes an initially tightly wound torsion spring which urges the sector in a brake-applying direction. When the control is being installed in a vehicle, the sector is locked against being turned by the spring. After the control has been installed and the brake cable has been connected to the sector, the sector is unlocked and is automatically rotated by the tightly wound spring until the slack in the cable is taken up and the cable is tensioned sufficiently to preload the return springs of the parking brake. In this way, the cable and the return springs are placed under a specified preload by the torsion spring once the cable has been hooked up and the sector has been released to the action of the torsion spring.
A push-to-release parking brake control is one which effects release of the parking brake when the foot-operated pedal is again depressed after the brake has been set. Depression of the pedal releases the pawl from the sector an allows release of the brake.
Self-adjusting, push-to-release parking brake controls are known. One such control requires two sectors. One of the sectors coacts with a pawl to perform the holding and push-to-release functions while the other sector is required to enable the control to self-adjust.
Significant input force is required to set the brake. In order to generate such force with relatively low manual effort, the control is equipped with a curved cam which acts against the cable to produce a mechanical advantage. In the two-sector control discussed above, the cam is carried by one of the sectors and produces a mechanical advantage of fixed ratio. That is to say, the mechanical advantage is constant throughout the entire operating range of the control. As a result, relatively low-effort is required to set the brake lightly but significantly greater effort is required to set the brake to its fully applied condition.